The introduction of genetically modified organisms (GMOs) has called
for an improved understanding of the fate of DNA in various environments,
because extracellular DNA may also be important for transferring genetic
information between individuals and species. Accumulating nucleotide
sequence data suggest that acquisition of foreign DNA by horizontal gene
transfer (HGT) is of considerable importance in bacterial evolution. The
uptake of extracellular DNA by natural transformation is one of several ways
bacteria can acquire new genetic information given sufficient size,
concentration and integrity of the DNA. We review studies on the release,
breakdown and persistence of bacterial and plant DNA in soil, sediment and
water, with a focus on the accessibility of the extracellular nucleic acids
as substrate for competent bacteria. DNA fragments often persist over time
in many environments, thereby facilitating their detection and
characterization. Nevertheless, the long-term physical persistence of DNA
fragments of limited size observed by PCR and Southern hybridization often
contrasts with the short-term availability of extracellular DNA to competent
bacteria studied in microcosms. The main factors leading to breakdown of
extracellular DNA are presented. There is a need for improved methods for
accurately determining the degradation routes and the persistence, integrity
and potential for horizontal transfer of DNA released from various organisms
throughout their lifecycles.